Device-to-device (d2d) communications

ABSTRACT

Technology for performing device-to-device (D2D) communications is disclosed. A user equipment (UE) can identify D2D data to be transmitted from the UE. The D2D data can be identified when the UE is in a radio resource control (RRC) idle. The UE can be limited to using a defined resource allocation mode to transmit the D2D data from the UE. A service request procedure can be initiated at the UE. The service request procedure can trigger the UE to perform an RRC connection establishment procedure with an evolved node B (eNB) to switch the UE from the RRC idle mode to an RRC connected mode. The UE can receive an uplink (UL) grant from the eNB for communicating the D2D data from the UE. The UE can send the D2D data using the UL grant provided by the eNB.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/583,030 filed Dec. 24, 2014 with attorney docket no. P67658 whichclaims priority to U.S. Provisional Patent Application No. 61/990,679,filed May 8, 2014 with attorney docket no. of P67658Z, the entirespecification of which is hereby incorporated by reference in itsentirety for all purposes.

BACKGROUND

Wireless mobile communication technology uses various standards andprotocols to transmit data between a node (e.g., a transmission station)and a wireless device (e.g., a mobile device). Some wireless devicescommunicate using orthogonal frequency-division multiple access (OFDMA)in a downlink (DL) transmission and single carrier frequency divisionmultiple access (SC-FDMA) in an uplink (UL) transmission. Standards andprotocols that use orthogonal frequency-division multiplexing (OFDM) forsignal transmission include the third generation partnership project(3GPP) long term evolution (LTE), the Institute of Electrical andElectronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m),which is commonly known to industry groups as WiMAX (Worldwideinteroperability for Microwave Access), and the IEEE 802.11 standard,which is commonly known to industry groups as WiFi.

In 3GPP radio access network (RAN) LTE systems, the node can be acombination of Evolved Universal Terrestrial Radio Access Network(E-UTRAN) Node Bs (also commonly denoted as evolved Node Bs, enhancedNode Bs, eNodeBs, or eNBs) and Radio Network Controllers (RNCs), whichcommunicates with the wireless device, known as a user equipment (UE).The downlink (DL) transmission can be a communication from the node(e.g., eNodeB) to the wireless device (e.g., UE), and the uplink (UL)transmission can be a communication from the wireless device to thenode.

In homogeneous networks, the node, also called a macro node, can providebasic wireless coverage to wireless devices in a cell. The cell can bethe area in which the wireless devices are operable to communicate withthe macro node. Heterogeneous networks (HetNets) can be used to handlethe increased traffic loads on the macro nodes due to increased usageand functionality of wireless devices. HetNets can include a layer ofplanned high power macro nodes (or macro-eNBs) overlaid with layers oflower power nodes (small-eNBs, micro-eNBs, pico-eNBs, femto-eNBs, orhome eNBs [HeNBs]) that can be deployed in a less well planned or evenentirely uncoordinated manner within the coverage area (cell) of a macronode. The lower power nodes (LPNs) can generally be referred to as “lowpower nodes”, small nodes, or small cells.

In LTE, data can be transmitted from the eNodeB to the UE via a physicaldownlink shared channel (PDSCH). A physical uplink control channel(PUCCH) can be used to acknowledge that data was received. Downlink anduplink channels or transmissions can use time-division duplexing (TDD)or frequency-division duplexing (FDD).

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the disclosure will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the disclosure; and, wherein:

FIG. 1 illustrates a legacy technique for establishing a radio resourcecontrol (RRC) connection for a user equipment (UE) in accordance with anexample;

FIG. 2 illustrates establishing a radio resource control (RRC)connection for a user equipment (UE) to enable the UE to perform adevice-to-device (D2D) communication in accordance with an example;

FIG. 3 illustrates configuring a user equipment (UE) to perform adevice-to-device (D2D) communication when the UE is in a radio resourcecontrol (RRC) connected mode with an evolved node B (eNB) in accordancewith an example;

FIG. 4 illustrates signaling between a user equipment (UE) and anevolved node B (eNB) for configuring the UE to perform adevice-to-device (D2D) communication in accordance with an example;

FIG. 5 illustrates an abstract syntax notation (ASN) code example ofaccess class barring parameters for device-to-device (D2D)communications in a system information block 2 (S1B2) message inaccordance with an example;

FIG. 6 illustrates functionality of a user equipment (UE) operable toperform device-to-device (D2D) communications in accordance with anexample;

FIG. 7 illustrates functionality of a user equipment (UE) operable toperform device-to-device (D2D) communications in accordance with anexample;

FIG. 8 depicts a flowchart of a method for performing device-to-device(D2D) communications in accordance with an example; and

FIG. 9 illustrates a diagram of a wireless device (e.g., UE) inaccordance with an example.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular examples only and is not intended to be limiting. The samereference numerals in different drawings represent the same element.Numbers provided in flow charts and processes are provided for clarityin illustrating steps and operations and do not necessarily indicate aparticular order or sequence.

Example Embodiments

An initial overview of technology embodiments is provided below and thenspecific technology embodiments are described in further detail later.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key features oressential features of the technology nor is it intended to limit thescope of the claimed subject matter.

A technology is described for performing device-to-device (D2D)communications at a user equipment (UE). The UE can operate according toLTE/E-UTRAN related standards, or the UE can operate in a cellularmobile network according to the 3GPP LTE Release 12 (or earlier)standard for E-UTRAN. In one example, the UE that is sending D2D datacan be referred to as a sending UE and the UE that is receiving the D2Ddata can be referred to as a destination UE, target UE, or a receivingUE. The D2D data can be generated by a D2D application that is runningon the UE. The UE can identify that the D2D data is to be transmitted tothe target UE using a D2D radio bearer of the UE. In one example, theD2D data can be sent from the sending UE to a single target UE or agroup of target UEs. The D2D application can generate the D2D data tosend to the target UE when the UE is in a radio resource control (RRC)idle mode. In addition, the D2D radio bearer of the UE can be presentwhen the UE is in the RRC idle mode, but cellular radio bearers (or dataradio bearers) may not be established when the UE is in the RRC idlemode.

In order for the UE to send the D2D data to the target UE, the UE cantransition into an RRC connected mode. The UE can determine that adefined resource allocation mode is to be used for communicating the D2Ddata to the target mode. The UE can determine the defined resourceallocation mode based on system information block (SIB) broadcast fromthe eNB. In one example, the defined resource allocation mode can be D2Dresource allocation mode 1. A service request procedure can be initiatedat a non-access stratum (NAS) of the UE. The service request procedurecan trigger an RRC layer of the UE to perform an RRC connectionestablishment procedure with the eNB. The UE can switch from the RRCidle mode to an RRC connected mode upon completion of the RRC connectionestablishment procedure. The UE, now in the RRC connected mode, can senda buffer status report (BSR) to the eNB, and in response, the UE canreceive an uplink (UL) grant from the eNB for transmission of the D2Ddata to the target UE. The UE can send the D2D data to the target UEusing the UL grant provided by the eNB. The D2D data can be transmittedto the target UE using the D2D radio bearer of the UE.

In an alternative configuration, the D2D data can be generated by theD2D application that is running on the UE when the UE is already in theRRC connected mode. In other words, the cellular radio bearers canalready be established for the UE, as well as the D2D radio bearers. TheUE can determine that the defined resource allocation mode (e.g., D2Dresource allocation mode 1) is to be used for communicating the D2D datato the target mode. The UE can send an RRC configuration request messageto the eNB using a signaling radio bearer of the UE, and in response,the UE can receive an RRC connection reconfiguration message from theeNB. The RRC connection reconfiguration message can include one or moreconfiguration parameters for the defined resource allocation mode. Someexamples of these configuration parameters can include a periodic D2DBSR timer or a D2D BSR retransmission timer. The UE can send a bufferstatus report (BSR) to the eNB using the one or more configurationparameters. In response, the UE can receive an uplink (UL) grant fromthe eNB for transmission of the D2D data to the target UE. The UE cansend the D2D data to the target UE using the UL grant provided by theeNB. In addition, the UE can send the D2D data using the D2D radiobearers of the UE.

Device to device (D2D) communication for 3GPP LTE networks, such as anEvolved Universal Terrestrial Radio Access network (E-UTRAN), is beingstandardized in 3GPP LTE Release 12. A D2D communication is a directcommunication between two devices, such as two user equipments (UEs).The two devices (e.g., LTE-based devices) can communicate directly withone another when the two devices are in close proximity, but such D2Dcommunications do not use the cellular network infrastructure. Oneparticular application for D2D communications is related to publicsafety services. Furthermore, D2D communication can allow directcommunication from one UE to one or more target or receiving UEs, thusenabling group communication. Examples described herein can refer totransmission to a target or receiving UE, but it should be understoodthat this could also be a transmission to a group of target or receivingUEs.

D2D can allow a direct link between two UEs that are using the cellularspectrum. As a result, media or other data can be transferred from onedevice to another device over short distances and using a directconnection. By using D2D data communications, the data can becommunicated directly without being relayed to the cellular network,thereby avoiding problems with lack of or poor network coverage or withoverloading the network. The cellular infrastructure, if present canassist with other issues, such as peer discovery, synchronization, andthe provision of identity and security information.

The use of D2D communication can provide several benefits to users. Forexample, the devices can be remote from cellular infrastructure. D2D canallow devices to communicate locally, even when the cellular network hasfailed (e.g., during a disaster) because D2D communication does not relyon the network infrastructure. By using licensed spectrum, thefrequencies used to perform the D2D communications are less subject tointerference. In addition, if the two devices are in close proximity,then reduced transmission power levels are used, thereby saving power atthe devices.

D2D communication features can be referred to as ProSe (ProximityServices) Direct Commination in the 3GPP LTE standard. D2Dcommunications are primarily targeted for public safety use cases, butcan be used for other applications as well. The D2D feature enables thedirect communication between UEs over the cellular radio spectrum, butwithout the data being carried by the cellular network infrastructure.D2D communication can occur when the UE is outside of the coverage ofthe cellular network, or alternatively, when the UE in within coverageof the cellular network. Within the access stratum of the UE, the D2Ddata can be carried by a D2D radio bearer.

While D2D radio bearers are similar to the radio bearers used forcellular communication, there are several key differences. For example,a D2D radio bearer can exist in the UE when the UE is in either a radioresource control (RRC) idle mode or an RRC connected mode. In otherwords, the D2D radio bearer can exist when the UE is in either RRC_IDLEmode or RRC_CONNECTED mode. In contrast, cellular radio bearers (or dataradio bearers) can only exist when the UE is in the RRC connected mode.In addition, D2D radio bearers can be created and released by the UE asnecessary based on the arrival of data from application layers of theUE. In contrast, cellular radio bearers are created, configured andreleased by the network.

When the UE is within the coverage of the cellular network, it can bebeneficial to coordinate D2D transmissions from the UE with other UEtransmissions in the cell in order to avoid the D2D transmissionscausing interference into the normal cellular communication. In otherwords, when two devices are attempting to perform the D2D communicationwithin the coverage of the cellular network, the cellular activity onthe radio spectrum can be coordinated with the D2D activity on the sameradio spectrum. When the UE transmits D2D data to another UE, the D2Ddata is transmitted on the same carrier frequency as the UE would use totransmit to the network. In addition, D2D transmissions and D2Dreceptions can occur on the uplink portion of the network's spectrum.Therefore, the UE transmits or receives D2D data on what would normallybe the uplink of the UE's transmit spectrum. Since the network canschedule uplink transmissions for various UEs in the cell, the networkhas to ensure that these D2D transmissions do not collide orinterference with uplink transmissions from the UE that are scheduled bythe network (since the cellular activity and the D2D activity occur onthe same spectrum).

In one example, the coordination between the cellular activity and theD2D activity can be achieved using D2D resource allocation mode 1, inwhich the transmitting UE requests transmission resources for D2Dtransmissions from the network. The UE can request the transmissionresources in a manner similar to when the UE requests transmissionresources for typical UE-to-network transmissions. For example, arequest for transmission resources can typically occur by the UE sendinga media access control (MAC) layer buffer status report (BSR) to anevolved node B (eNB), and the eNB can respond with the assignedresources in the form on an uplink (UL) grant signaled within thephysical layer.

In D2D resource allocation mode 1, the eNB can be actively involved inscheduling the time and frequency at which the UE performs the D2Dtransmissions. In an alternative scenario, the UE can perform the D2Dtransmissions using a D2D resource allocation mode 2, in which the UE ismore autonomous in performing the D2D transmissions. D2D resourceallocation mode 2 may occur when the UE is outside coverage of the eNB,but can also occur when the UE is within coverage. In mode 2, the eNBcan reserve a certain potion of its resources and then allows the UE toautonomously choose where to transmit D2D data within that reservedportion. Since the resources are reserved for the D2D communications ina rather static manner, a waste of resources can occur when all of thereserved resources are not be used. In contrast, D2D resource allocationmode 1 allows the network to dynamically allocate resources when D2Dtransmissions are imminent, thereby providing a more efficient solution.If there are no UEs that desire to perform D2D transmissions, thenresources are not unnecessarily assigned for D2D transmissions andavailable for normal cellular communications.

In one example, D2D resource allocation mode 1 can be used when the UEis in RRC_CONNECTED. In other words, there is an active connectionbetween the UE and the eNB. In addition, the UE is to remain inRRC_CONNECTED for the duration of the D2D activity. The eNB can use thisconnection for assigning resources to the UE to enable the UE to performthe D2D transmissions. The UE is to be in RRC_CONNECTED because both theMAC layer and the physical layer signaling can rely on the UE having anassigned Cell Radio Network Temporary Identifier (C-RNTI). In addition,the UE being in RRC_CONNECTED can allow the eNB to configure the UE withparameters to control the UE's buffer status reporting behavior.However, traditional processes for transitioning the UE from an RRC idlemode to the RRC connected mode involving both the non-access stratum(NAS) and access stratum (AS) layers is not suitable for the D2Dscenario.

FIG. 1 illustrates a legacy technique for establishing a radio resourcecontrol (RRC) connection fora user equipment (UE) 140. When the UE 140has cellular data to send to the network, a number of steps can beperformed by entities within the UE 140 in order to move the UE 140 froma radio resource control (RRC) idle mode to an RRC connected mode. TheUE 140 can communicate the data to an evolved node B (eNB) upontransitioning into the RRC connected mode. The entities within the UE140 can include applications 120, an Internet Protocol (IP) stack 122, aradio access bearer (RAB) manager 124, a non-access stratum (NAS) layer126, an RRC layer 128, signaling radio bearers 130, cellular radiobearers 132 and a physical layer 134.

The UE 140 can initially be in RRC idle mode. When the UE 140 is in theRRC idle mode, no cellular radio bearers (or data radio bearers) existand no user data can be transferred from the UE 140 to the network.

In step 102, an application 120 in the UE 140 can generate user data fortransmission. The application 120 can pass the data to the IP stack 122for transmission, wherein the data is then passed to the RAB manager124.

In step 104, the RAB manager 124 can track whether appropriate radiobearers exist in the UE 140. When the RAB manager 124 detects that noradio bearers are established for the UE 140, the RAB manager 124 cansend a request to the NAS layer 126 for creation of the radio bearers.

In step 106, the NAS layer 126 can initiate a service request procedurethat requests the network to establish the radio bearers. In order toperform the service request procedure, the NAS 126 can provide a servicerequest message to the RRC layer 128 in the access stratum. The servicerequest message can request establishment of an RRC connection for theUE 140.

In step 108, the RRC layer 128 can perform an RRC connectionestablishment procedure with the eNB, which can result in creation ofthe signaling radio bearer 130. The signaling radio bearer 130 can beused to send a NAS service request message to the network.

In step 110, in response to receiving the NAS service request message,the network can initiate various actions for establishing the cellularradio bearers 132 (or data radio bearers) for the UE 140. For example,the network can instruct the UE 140, via RRC signaling, to establish thecellular radio bearers 132 and then the RRC 128 can setup those cellularradio bearers 132 in the UE 140. User data can subsequently transmittedfrom the UE to the network using the cellular radio bearers 132.Therefore, when no radio bearers are established for the UE 140, the UE140 is to enter into an RRC connected mode for creation of those radiobearers. In addition, the network can perform other actions, such as anestablishment of security for the UE 140.

The process described above for establishing the RRC connection for theUE is not directly suitable for D2D communication. In contrast tocellular radio bearers, the D2D radio bearers can already exist when theUE is in idle mode, e.g., because the UE was using the D2D radio bearerswhile it was out of network coverage. Thus, the RAB manager function inthe legacy system, which triggers the NAS to perform the service requestwhenever there is data to be sent but there are no established radiobearers, is difficult to apply to D2D. The decision on whether the UE isto use D2D resource allocation mode 1, and therefore be moved intoRRC_CONNECTED, can depend on access stratum specific information thatwould not normally be available to the NAS layer when deciding totrigger the service request procedure.

In previous solutions, the RAB manager can request the NAS to establishthe radio bearers, which in turn causes the NAS to request establishmentof the RRC Connection. However, this previous solution is not directlyapplicable to the D2D case because the D2D radio bearers can alreadyexist. In other words, the D2D radio bearers can already be in use whenthe UE determines that D2D resource allocation mode 1 is to be used. TheD2D radio bearers can exist even when the UE is in the RRC idle mode. Inone example, the UE could initially be out of network coverage and usingD2D resource allocation mode 2 for D2D transmission, whereby the UEautonomously selects transmission resources from a configured pool ofresources. The UE can subsequently move into network coverage of a cellin which D2D resource allocation mode 1 is to be used. However, the D2Dbearers were previously established when the UE was outside of networkcoverage, and the UE does not have to reestablish the D2D bearers uponentering into network coverage. Therefore, the previous function of theRAB manager (e.g., observing data that arrives and initiatingappropriate protocols for establishing an RRC connection when radiobearers do not exist for the UE) do not directly apply when the D2Dradio bearers are already existent at the UE.

The technology described herein is for establishing an RRC connectionfor the UE to enable the UE to perform D2D communication. For example,the UE can perform the D2D communication with a target UE. When the UEis in an RRC idle mode, D2D data for transmission on a D2D radio bearercan be received at the UE from upper layers (e.g., from an applicationrunning on the UE). The UE can check certain conditions to determinewhether D2D resource allocation mode 1 is to be used. If mode 1 does notneed to be used, then the UE can transmit the data to the target UE viathe D2D radio bearer (even when the UE is in RRC idle mode). On theother hand, if mode 1 is to be used for communicating the data, then aUE access stratum can request a UE NAS to move the UE from the RRC idlemode into an RRC connected mode. The UE NAS can initiate a servicerequest procedure to move the UE from the RRC idle mode to the RRCconnected mode. In a configuration that is alternative to the servicerequest procedure, the UE NAS can initiate a tracking area updatingprocedure with an “active” flag set in a tracking area update request,which can enable establishment of the RRC connection for the UE.

In one example, whether the UE is to transition to the RRC connectedmode in order to perform the D2D transmission can depend on a type ofresource allocation being used in the network. For example, the UE is tomove into the RRC connected mode when the network is using D2D resourceallocation mode 1. On the other hand, the UE may not enter the RRCconnected mode when the network is using D2D resource allocation mode 2.

FIG. 2 illustrates establishing a radio resource control (RRC)connection for a user equipment (UE) 250 to enable the UE 250 to performa device-to-device (D2D) communication. When the UE 250 has D2D data tosend to another UE (e.g., a target UE or a receiving UE), a number ofsteps can be performed by entities within the UE 250 in order to movethe UE 250 from a radio resource control (RRC) idle mode to an RRCconnected mode. The UE 250 can move to the RRC connected mode when theUE 250 is to use D2D resource allocation mode 1 to perform the D2Dtransmission. Upon moving into the RRC connected mode, the UE 250 canrequest resources to transmit the D2D data to the target UE. Theentities within the UE 250 can include applications 220, an InternetProtocol (IP) stack 222, a non-access stratum (NAS) layer 226, an RRClayer 228, signaling radio bearers 230, a physical layer 234, D2D radiobearers 236, a media access control (MAC) layer 238, and a D2D MAC layer240. In this example, the UE 250 may not include a radio access bearer(RAB) manager. Alternatively, the UE 250 may include the RAB manager,but the RAB manager is not used for performing D2D transmissions.

The UE 250 can initially be in RRC idle mode. When the UE 140 is in theRRC idle mode, no cellular radio bearers exist and no user data can betransferred from the UE 140 to the network. However, D2D radio bearersmay exist for the UE 250. The D2D radio bearers may have already beenused by the UE 250 for transmitting and receiving D2D data.

In step 202, an application 220 in the UE 250 can generate user D2D datafor transmission. The application 220 can pass the D2D data to the IPstack 222 for transmission. The IP stack 222 can pass the D2D data tothe D2D radio bearers 236 for transmission and the D2D radio bearers 236can notify the MAC layer 238, or more specially the D2D MAC 240functionality in the MAC layer, that there is D2D data pending fortransmission.

In step 204, the MAC layer 238 of the UE 240 can indicate to the RRClayer 228 that D2D data is pending transmission. In one example, the MAClayer 228 is a single entity that is used by all radio bearers to accessthe radio. The D2D MAC 240 can represent the functionality of the MAClayer 238 that is related to D2D communication. In alternative examples,other layers within the UE 250 can indicate the pending D2D datatransmission to the RRC layer 228, such as a radio link control (RLC)layer or a packet data convergence protocol (PDCP) layer within the UE250.

In step 206, prior to transmission of the D2D user data, the RRC layer228 of the UE 250 can check whether the UE 250 is to use D2D resourceallocation mode 1 or whether the UE 250 can use resource allocation mode2. In one example, the UE 250 can determine which mode is to be usedbased on a system information block (SIB) message previously broadcastedfrom the network. If the UE 250 determines that resource allocation mode1 is to be used, then the RRC layer 228 can request the NAS layer 226 tomove the UE 250 into the RRC connected mode. In other words, if resourceallocation mode 1 is to be used, then the UE 250 is to enter the RRCconnected mode in order for the D2D data transmission to occur.

In step 208, the NAS layer 226 of the UE 250 can receive the request tomove the UE 250 into the RRC connected mode from the RRC layer 228 ofthe UE 250. The NAS layer 226 can initiate a service request procedure.The service request procedure can result in an establishment of thecellular radio bearers for the UE 250. In order to perform the servicerequest procedure, the NAS layer 226 can provide a service requestmessage to the RRC layer 228 in the access stratum. The service requestmessage from the NAS layer 226 can request the RRC layer 228 toestablish an RRC connection for the UE 250. In an alternative example,rather than performing the service request procedure, the NAS layer 226of the UE can initiate a tracking area updating procedure with “active”flag set in the tracking area update request. As a result, the RRC layer228 of the UE 250 can be notified to establish the RRC connection forthe UE 250.

In step 210, the RRC layer 228 of the UE 250 performs an RRC connectionestablishment procedure with an evolved node B (eNB). As a result, theRRC connection can be established for the UE 250 and the signaling radiobearer 230 for the UE 250 can be created. In other words, the UE 250 canswitch to being in the RRC connected mode upon completion of the RRCconnection establishment procedure. The signaling radio bearer can thenbe used to send a NAS Service Request message to the network.

In step 212, once the UE 250 is in the RRC connected mode, the RRC layer228 can indicate to the MAC layer 238 that the UE 250 is inRRC_CONNECTED. The RRC layer 228 can indicate that the UE 250 is toproceed with performing a D2D transmission using D2D resource allocationmode 1. This indication can include various configuration parametersthat are specific to D2D resource allocation mode 1. For example, theindication from the RRC layer 228 to the MAC layer 238 can include aperiodic D2D BSR timer and a D2D BSR retransmission timer. In oneexample, the RRC layer 228 can receive the various configurationparameters that are specific to D2D resource allocation mode 1 from theeNB upon establishment of the RRC connection. The UE 250 can now use theD2D resource allocation mode 1 for sending MAC layer buffer statusreports (BSRs) to the eNB. In other words, the MAC layer 238 can sendthe BSRs to the eNB using the various configuration parameters (e.g.,periodic D2D BSR timer, D2D BSR retransmission timer). The eNB canrespond with uplink (UL) grants, and thereafter, the UE 250 can transmitthe D2D data using those UL grants. In other words, the UL grants caninform the UE 250 at which time and at which frequency the UE 250 is toperform the D2D transmission, such that the UE's D2D transmission doesnot coincide with other previously scheduled cellular transmissions(i.e., data sent from the UEs to the network). This process can involveusing the D2D radio bearers to perform the D2D transmission (i.e., notthe cellular radio bearers), and substantially no further interactionneeds to occur between the NAS layer 226 and the RRC layer 228. The UE250 can continue to use this process for as long as the UE 250 has D2Ddata to transmit and remains in RRC_CONNECTED.

In step 214, in response to receiving the NAS Service Request message,the network can initiate various actions for establishing the cellularradio bearers. However, establishment of the cellular radio bearers donot affect the D2D data that is sent using the D2D bearers. An exampleaction can include establishing access stratum security, which protectsthe signaling radio bearer 230, as well as cellular radio bearers thatare subsequently established. However, the access stratum security isnot used to protect the D2D radio bearers, which have a separatesecurity protection that can operate irrespective of whether the UE 250is in RRC_IDLE or RRC_CONNECTED. In addition, the network can instructthe UE 250, via RRC signaling, to establish the cellular radio bearers.The RRC layer 228 of the UE 250 can subsequently function to set upthose cellular radio bearers.

In some examples, determining whether the UE is restricted in usingresource allocation mode 1 can be performed in a number of manners. Forexample, if the UE is camped on a suitable cell (i.e., implying that theUE is within network coverage) then resource allocation mode 1 is to beused. In another example, if a signal level is above a configuredthreshold, then resource allocation mode 1 is to be used. The signallevel can be based on reference symbol received power (RSRP)measurements or reference symbol received quality (RSRQ) measurements.In yet another example, whether the serving cell indicates in systeminformation that D2D communication is supported within the servingcell's coverage can be determined. This indication can be implicitlyindicated by the presence of a system information block (SIB) that isspecific to D2D, or it could be implicitly indicated by the presence ofspecific D2D related parameters with the system information. Forexample, this indication can be implicitly indicated by the presence ofD2D resource pool information. In addition, the system information fromthe serving cell can explicitly indicate that the UE is restricted tousing resource allocation mode 1 within that serving cell. The systeminformation can be broadcast from the eNB to the UE. In an additionalexample, the serving cell can indicate that D2D UEs are to establish aconnection with the eNB (i.e., move into the RRC connected mode), uponwhich the UE is informed via dedicated signaling from the eNB of whetherthe UE is to use D2D resource allocation mode 1 or mode 2. In thisapproach, the eNB can determine whether the UE is to use D2D resourceallocation mode 1 or mode 2, rather than the UE.

As previously discussed, the MAC layer can inform the RRC layer of thepending D2D data transmission. The RRC layer can evaluate certainconditions (e.g., whether the UE is to use resource allocation mode 1),and depending on whether these conditions are satisfied, the RRC layercan request the NAS layer to be moved into the RRC connected mode. Inalternative configurations, these conditions can be evaluated in otherlocations within the UE, such as the PDCP layer, the MAC layer or withinan upcoming layer or function within the UE. In addition, the evaluationof the conditions can be distributed between different entities withinthe UE.

As previously discussed, the UE can determine that resource allocationmode 1 is to be used, and as a result, the RRC layer can request the NASlayer to move the UE into RRC_CONNECTED. In an alternative scenario, theUE can determine that D2D resource allocation mode 2 is to be used. Inthis case, the RRC layer can respond to the MAC layer with an indicationthat D2D resource allocation mode 2 is to be used, and the other stepsof the process described above are not relevant.

In one configuration, the UE does not determine to use D2D resourceallocation mode 1 or mode 2, but rather simply determines that the UE isto enter RRC_CONNECTED. In this case, the eNB can decide whether the UEis to use D2D resource allocation mode 1 or mode 2. This decision can beinformed to the UE in either a RRC CONNECTION SETUP message or an RRCCONNECTION RECONFIGURATION message. In particular, the eNB's decision onwhether the UE is to use D2D resource allocation mode 1 or mode 2 can becommunicated to the MAC layer of the UE.

In one configuration, the RRC does not determine that resourceallocation mode 1 is to be used and that an RRC connection is to beestablished for the UE. Rather, the RRC layer can provide an indicationto the NAS layer that an RRC connection may be needed for performing theD2D communication. In addition, the RRC layer can provide the NAS layerwith the necessary parameters to enable the NAS layer to decide whetherto initiate the service request procedure, and hence requestestablishment of the RRC connection. In other words, the NAS layer candetermine whether resource allocation mode 1 is to be used, as opposedto the RRC layer.

In one configuration, a purpose for moving the UE from RRC_IDLE modeinto RRC_CONNECTED mode can be included in messaging between the MAClayer, the NAS layer and/or the RRC layer. This purpose (i.e., D2Dtransmission) can also be provided to the eNB, either within a RRCconnection request message (e.g., as a novel ‘establishment cause’ valuesuch as ‘D2D’ or ‘D2D communication’), or in a RRC connection setupcomplete message (e.g., in a novel ‘D2D transmission request’information element). The RRC connection request message and the RRCconnection setup complete message can both be part of the RRC connectionestablishment procedure. An advantage of including such an indicator isthat the eNB can learn that the UE is to use D2D resource allocationmode 1, and hence the eNB can automatically provide applicableconfiguration parameters associated with resource allocation mode 1. Inone example, the eNB can provide the configuration parameters (e.g., aperiodic D2D BSR timer, a D2D BSR retransmission timer) in a RRconnection reconfiguration message. Another advantage of using a novelD2D specific establishment cause in the RRC connection request messageis that, in cases where the eNB is under heavy load, the eNB canprioritize or deprioritize connection establishments for the purpose ofD2D communication. For example, if D2D is being used by public safetyusers within a network, then the eNB can choose to accept connectionestablishments for D2D purposes. On the other hand, if D2D is being usedas a service by non-public safety users within the network, then the eNBcan choose to reject connection establishments for D2D purposes.

In one example, the establishment of the cellular radio bearers (or dataradio bearers) is not essential for the purpose of transmitting D2D userdata. In other words, the D2D transmission can be successfully performedupon receiving uplink grants from the eNB, wherein the uplink grantsindicate certain times at which the UE is allowed to perform the D2Dtransmission. However, using a legacy service request procedure canresult in the cellular radio bearers being established, even thoughthere is no cellular data waiting to be transmitted.

In one configuration, the NAS layer can initiate a tracking area updateprocedure (without the ‘active’ flag set) instead of the service requestprocedure. The tracking area update procedure can result in the UE beingmoved into RRC_CONNECTED without the cellular radio bearers beingestablished. This configuration can be advantageous because the cellularradio bearers are not essential for the purpose of transmitting D2D userdata, and hence non-essential operations can be avoided. However, thisconfiguration can also be disadvantageous because access stratumsecurity would not be started, and as a result, the RRC signaling on thesignaling radio bearer would not have security protection. In addition,handover of the RRC connection to another eNB would not be possiblebecause legacy versions of the 3GPP LTE specification only permithandover after the cellular user plane is established. Another aspect isthat the mobility management entity (MME) typically initiates release ofthe RRC connection shortly after the tracking area update procedure(without the active flag), which is in contrast to situations whencellular radio bearers have been established and then the eNB decides(typically based on lack of UE activity) when the RRC connection is tobe released.

In one configuration, the cellular radio bearers can be established forthe UE, and then the UE can send the buffer status reports (BSRs) usingthe various configuration parameters (e.g., periodic D2D BSR timerexpiry, a D2D BSR retransmission timer). In other words, the cellularradio bearers can be established before the UE receives the uplinkgrants from the eNB. This configuration can be advantageous because ifthe cellular radio bearers were to be established before the D2Dtransmission, then access stratum security can be established before theeNB sends RRC signaling including the configuration parameters relatedto the D2D resource allocation mode 1. The establishment of the accessstratum security before the eNB sends the RRC signaling can be apreference of the network operator.

FIG. 3 illustrates configuring a user equipment (UE) 350 to perform adevice-to-device (D2D) communication when the UE 350 is in a radioresource control (RRC) connected mode with an evolved node B (eNB). Whenthe UE 350 has D2D data to send to another UE (e.g., a target UE or areceiving UE), a number of steps can be performed by entities within theUE 350 in order to perform the D2D transmission. When the UE 350 has D2Ddata to send to the target UE, the UE 350 can already be inRRC_CONNECTED. However, the UE 350 may not be configured with parametersfor D2D resource allocation mode 1 (or mode 2), wherein the UE 350 is touse these parameters in order to perform the D2D transmission. Theentities within the UE 350 can include applications 320, an InternetProtocol (IP) stack 322, a non-access stratum (NAS) layer 326, an RRClayer 328, signaling radio bearers 330, a physical layer 334, D2D radiobearers 336, a media access control (MAC) layer 338, and a D2D MAC layer340.

The UE 350 can initially be in RRC connected mode. When the UE 350 is inthe RRC connected mode, cellular radio bearers can already exist for theUE 350. The UE 350 may have originally entered into the RRC connectedmode not to perform D2D transmissions, but rather to perform networktransmissions, i.e., with the evolved node B (eNB). After the UE 350 hasentered the RRC connected mode, the UE 350 can generate D2D data to besent to another UE. In addition, D2D radio bearers 336 may exist for theUE 350. The D2D radio bearers 336 may have already been used by the UE350 for transmitting and receiving D2D data at some previous point intime, but not during the current RRC connection. If the D2D radiobearers 336 had already been used during the current RRC connection,than the UE 350 may already be configured for D2D resource allocationmode 1 (or mode 2).

In step 302, an application 320 in the UE 350 can generate user D2D datafor transmission. The application 320 can pass the D2D data to the IPstack 322 for transmission. The IP stack 322 can pass the D2D data tothe D2D radio bearers 336 for transmission and the D2D radio bearers 336can notify the MAC layer 338, or more specially the D2D MAC 340functionality within the MAC layer, that there is D2D data pending fortransmission.

In step 304, the MAC layer 338 of the UE 350 can indicate to the RRClayer 328 that D2D data is pending transmission. In one example, the MAClayer 328 is a single entity that is used by all radio bearers to accessthe radio. The D2D MAC 340 can represent the functionality of the MAClayer 338 that is related to D2D communication. In alternative examples,other layers within the UE 350 can indicate the pending D2D datatransmission to the RRC layer 328, such as a radio link control (RLC)layer or a packet data convergence protocol (PDCP) layer within the UE350.

In step 306, the UE 350 can determine whether D2D resource allocationmode 1 is to be used, or if the UE 350 can use resource allocation mode2. The UE 350 can determine the appropriate resource allocation modebefore the D2D data is transmitted to the target UE. If the UE 350determines that resource allocation mode 1 is to be used, then the UE350 can send an RRC request to the network. For example, the RRC layer328 of the UE 350 can send the RRC request to the eNB. The requestmessage could be a novel message, such as a D2D resource request or aD2D configuration request. A D2D resource request indicator informationelement (IE) or a D2D configuration request indicator IE can be includedin the novel request message. Alternatively, the request message can bean existing message, such as UE ASSISTANCE INFORMATION containing anovel D2D resource request indicator information element (1E) ora D2Dconfiguration request indicator IE. The request message can be sent fromthe RRC layer 328 to the eNB using the signaling radio bearer (which isalready established because the UE 350 is in the RRC connected mode).

In an alternative configuration, the UE 350 does not determine whetherto use D2D resource allocation mode 1 or mode 2, but rather determinesto send the RRC request to the network. As a result, the eNB can decidewhether the UE 350 is to use D2D resource allocation mode 1 or mode 2.The eNB can inform the UE 350 of this decision via signaling from theeNB to the RRC layer 328. If the eNB were to inform the RRC layer 328that the UE 350 is to use D2D resource allocation mode 2, then the RRClayer 328 can inform the MAC layer 338 to use mode 2 when performing theD2D transmission.

In step 308, the eNB can respond to the RRC request from the RRC layer328 of the UE 350. The eNB can provide the UE 350 with necessaryconfiguration parameters for D2D resource allocation mode 1. Examples ofthese configuration parameters can include a periodic D2D BSR timer anda D2D BSR retransmission timer. In one example, the eNB can respond withthe configuration parameters in a RRC connection reconfigurationmessage. If the UE 350 is to use D2D resource allocation mode 2 forperforming the D2D transmission, then the RRC connection reconfigurationmessage can include an instruction to the UE 350 to use D2D resourceallocation mode 2.

In step 310, the RRC layer 328 can indicate to the MAC layer 338 thatthe UE 350 is in RRC_CONNECTED, and that the UE 350 is to proceed withperforming the D2D transmission using D2D resource allocation mode 1. Inaddition, the RRC layer 328 can provide the MAC layer 338 with thenecessary configuration parameters for using D2D resource allocationmode 1 to perform the D2D transmission. The UE 350 can use theconfiguration parameters for sending MAC layer buffer status reports(BSRs) to the eNB. In other words, the MAC layer 338 can send the BSRsto the eNB using the various configuration parameters (e.g., periodicD2D BSR timer, D2D BSR retransmission timer). The eNB can respond withuplink (UL) grants, and thereafter, the UE 350 can transmit the D2D datausing those UL grants. In other words, the UL grants can inform the UE350 at which time and at which frequency the UE 350 is to perform theD2D transmission, such that the UE's D2D transmission does not coincidewith other previously scheduled cellular transmissions (i.e., data sentfrom the UEs to the network).

FIG. 4 illustrates exemplary signaling between a user equipment (UE) 410and an evolved node B (eNB) 420 for configuring the UE 410 to perform adevice-to-device (D2D) communication. The UE 410 can send a D2Dconfiguration request message to the eNB 420. In one example, the D2Dconfiguration message can be sent to the eNB 420 using the UE'ssignaling radio bearer. The D2D configuration message can include a D2Dconfiguration request indicator information element (IE). The eNB 420can respond with an RRC connection reconfiguration message to the UE410. The RRC connection reconfiguration message can include various D2Dresource allocation mode 1 parameters, such as a periodic D2D BSR timerand a D2D BSR retransmission timer. In other words, thesereconfiguration parameters can allow the UE 410 to use D2D resourceallocation mode 1 for sending D2D transmissions. The UE 410 can send anRRC connection reconfiguration complete message to the eNB 420 inresponse to receiving the RRC connection reconfiguration message.

In one example, the UE 410 and the eNB 420 can perform a similar radiointerface message exchange as described above when the UE 410 isoriginally in RRC idle mode (as opposed to being in RRC connected mode).When the UE 410 is in the RRC idle mode, the UE 410 does not indicateits desire to perform a D2D communication to the eNB 420 as describedabove, that is in order to notify the eNB of the UE's desire to performthe D2D communication, the UE can use a novel ‘establishment cause’value in the RRC Connection Request message or a novel indicator in theRRC Connection Setup Complete message. Rather, once the UE 410 hassuccessfully entered RRC_CONNECTED, then the UE 410 can inform the eNB420 that it wishes to perform a D2D communication by sending an RRCrequest message (e.g., D2D CONFIGURATION REQUEST) to the eNB 420. Atthis point, the UE 410 can send the D2D configuration request message tothe eNB 420, the eNB 420 can send an RRC connection reconfigurationmessage to the UE 410, and the UE 410 can send an RRC connectionreconfiguration complete message to the eNB 420.

FIG. 5 illustrates an abstract syntax notation (ASN) code example ofaccess class barring (ACB) parameters for device-to-device (D2D)communications that can be included in a system information block 2(SIB2) message. In previous versions of the 3GPP LTE standard, thenetwork can restrict RRC connection setup request attempts by usingaccess class barring (ACB). As a part of D2D, it can be beneficial toextend this mechanism, such that the eNB can prohibit the UE fromsending a RRC connection request for purposes of D2D resourceallocation. ACB parameters specific to D2D can be added to the SystemInformation Block 2 (SIB2), as shown in FIG. 5. For example, a parameterof ac-BarringForD2D-r12 can be added to the SIB2 for setting up the ACBconfiguration.

With access class barring, the network may wish to set different barringconfigurations depending on whether the UE is accessing the network forthe purpose of D2D, or the whether the UE is accessing the network fornormal traffic purposes (e.g., voice calls, data transfers). If thenetwork is overloaded and D2D is being used by public safety users, thenD2D can be prioritized, but access barring can be applied to the non-D2Dtraffic. If the D2D is being used for other purposes (e.g., photosharing, video sharing), then UE-to-network traffic can be prioritizedinstead of device-to-device traffic.

If the UE receives the ACB configuration in S1B2, and evaluates thataccess to the cell is barred for a specific RRC Connection Establishmentattempt, then the RRC layer of the UE informs upper layers of the UEabout the failure to establish the RRC connection due to access barringfor D2D resource allocation being applied to the UE. In particular, theRRC layer can inform the upper layers of the ac-BarringForD2D parameterfrom the SIB2, upon which the RRC establishment procedure ends. In oneexample, the UE can use resource allocation mode 2 if the RRC connectionestablishment procedure cannot be successfully completed due to barring.In another example, support for resource allocation mode 1 can bedisabled via the system information block (SIB). In this example,changing the SIB (such that mode 1 is disabled) does not affect on-goingD2D transmissions, i.e., the UE which already uses resource allocationmode 1 in RRC connected mode can continue sending D2D BSRs for resourceallocation until the eNB configures the UE to use resource allocationmode 2 or releases the RRC connection.

In one configuration, the RRC connection can be released due toinactivity. In previous LTE systems, the eNB can trigger the release ofthe RRC Connection when it has observed inactivity on the cellular radiobearers (and sometimes the signaling radio bearers) for a certain periodof time, otherwise known as the “inactivity time”. With D2Dcommunication using resource allocation mode 1, the UE is to remain inRRC_CONNECTED for as long as the D2D communication is ongoing in orderto allow the UE to continue to request transmission resources. The eNBdoes not have any visibility of activity on the D2D radio bearers thatreside only within the UEs, and hence an eNB observing inactivity on thecellular radio bearers can mistakenly decide to release the RRCConnection of a UE before it has completed its D2D communication. Thisproblem can be addressed by the eNB observing D2D related MAC activity,such as the reception of a D2D BSR. Therefore, the RRC Connection for aparticular UE can be released when the eNB has observed inactivity onthe cellular radio bearers (and sometimes the signaling radio bearers)and no D2D BSR reception for a certain period of time. This additionalcondition for UE inactivity detection can be applied to those UEs whichthe eNB has configured to use D2D resource allocation mode 1.

Therefore, the RRC connection is not released due to inactivity of theUE, but rather inactivity at the eNB with respect to that particular UE.In previous systems, the eNB can release the RRC connection after adefined period of non-activity at the UE, but for D2D, the situation isdifferent because the eNB cannot actually observe the D2D communication.Since the D2D data is transferred directly between the UE and the targetUE, the eNB does not exactly know when the D2D transmission occurs.However, if the UE uses resource allocation mode 1, then the eNB candetect when the UE sends the buffer status reports (BSRs). The UE cansend the BSRs in order to request resources for performing the D2Dtransmissions. Thus, the eNB can indirectly determine (through the BSRs)whether the UE is actively sending D2D transmissions. If the eNB doesnot detect BSRs from the UE for a certain period of time, the eNB caninfer that the UE is inactive (in terms of D2D transmissions), and theeNB can release the RRC connection with the UE.

D2D discovery is a process whereby UEs can become aware of other UEsthat are within close proximity. The D2D discovery process can involvethe transmission of discovery signals and messages. The D2D discoveryprocess can be applicable when the UE is within coverage of the network.Similar to D2D communication resource allocation mode 1, D2D discoveryhas a resource allocation type 2 in which the UE is to be inRRC_CONNECTED in order to request transmission resources. Thus, similarmechanisms to those described above for D2D communication can apply tothe process of D2D discovery. However, a difference with D2D discoveryis that the D2D discovery protocol (also referred to as the ProSeDiscovery Protocol or the ProSe Protocol) resides outside of the accessstratum and may be more closely linked to the NAS protocols. Therefore,the D2D discovery protocol can directly request the NAS to initiate aprocedure to move the UE to RRC_CONNECTED prior to the D2D discoveryprotocol generating messages, rather than using the arrival of thosemessages within the access stratum to trigger the process.

The conditions for whether the UE is to enter RRC_CONNECTED can includevarious access stratum parameters that are typically not available tothe NAS. These parameters can be from system information, such as anindication of whether the UE is to use D2D discovery resource allocationtype 1 or type 2. Since the NAS does not typically have theseparameters, the RRC layer can provide these parameters to the NAS layer.Thus, the NAS layer can determine whether to use D2D discovery resourceallocation type 1 or type 2 prior to initiating a service requestprocedure. Alternatively, the RRC layer can provide these parameters tothe D2D discovery protocol, so that the D2D discovery protocol candetermine whether the UE is to use D2D discovery resource allocationtype 1 or type 2 prior to requesting the NAS to initiate the RRCconnection setup procedure.

In one example, the UE can perform cell selection or reselection byperforming measurements on neighboring cells, and then attempting toreselect the cells that operate on a frequency with a highest priority.An indication for which frequency (or frequencies) has the highestpriority can be provided to the UE via a system information block (SIB)or through dedicated signaling. This cell reselection priority can beused to manage radio access technologies (RATs), carrier frequency orcell loading in different deployment scenarios. However, D2D may not besupported in all carrier frequencies. Based on the operator's decision,the cells of some carrier frequencies may support D2D, and the operatorcan assign a resource pool for D2D in those cells. In this case, it canbe beneficial for the D2D UE to consider whether a particular carrierfrequency supports D2D when the UE performs cell reselection. Forexample, the UE can prioritize the frequency layer supporting D2D. Theinformation on whether D2D is supported can be included ininter-frequency cell reselection information in SIB5. In anotherexample, the UE can be preconfigured with a list of carrier frequenciessupporting D2D, wherein the list can be previously provided by a D2Dserver. In yet another example, the UE can prioritize carrierfrequencies based on whether D2D is supported only when D2D operation isenabled at the UE. Otherwise, the UE can follow a default priorityscheme (i.e., a priority scheme in which the UE does not reselect cellsbased on whether a particular cell supports D2D operation).

Another example provides functionality 600 of a user equipment (UE)operable to perform device-to-device (D2D) communications, as shown inthe flow chart in FIG. 6. The functionality can be implemented as amethod or the functionality can be executed as instructions on amachine, where the instructions are included on at least one computerreadable medium or one non-transitory machine readable storage medium.The UE can include one or more processors configured to identify D2Ddata to be transmitted from the UE using a D2D radio bearer of the UE,the D2D data being identified when the UE is in a radio resource control(RRC) idle mode, as in block 610. The UE can include one or moreprocessors configured to determine that the UE is limited to using adefined resource allocation mode to communicate the D2D data from theUE, as in block 620. The UE can include one or more processorsconfigured to initiate a service request procedure at a non-accessstratum (NAS) of the UE, the service request procedure triggering an RRClayer of the UE to perform an RRC connection establishment procedurewith an evolved node B (eNB) to switch the UE from the RRC idle mode toan RRC connected mode, as in block 630. The UE can include one or moreprocessors configured to receive an uplink (UL) grant from the eNB fortransmission of the D2D data from the UE, as in block 640. The UE caninclude one or more processors configured to send the D2D data using theUL grant provided by the eNB, the D2D data being transmitted from the UEusing the D2D radio bearer of the UE, as in block 650.

In one example, the one or more processors can be further configured toreceive the UL grant from the eNB in response to sending a buffer statusreport (BSR) from a medium access control (MAC) layer of the UE to theeNB, the BSR being sent to the eNB after the UE has switched to the RRCconnected mode. In another example, the one or more processors can befurther configured to use one or more configuration parametersassociated with the defined resource allocation mode for sending the BSRfrom the MAC layer of the UE to the eNB, the one or more configurationparameters including at least one of a periodic D2D BSR timer or a D2DBSR retransmission timer.

In one example, the one or more processors can be further configured toperform the RRC connection establishment procedure at the RRC layer ofthe UE in order to create a signaling radio bearer for the UE. Inanother example, the one or more processors are further configured tosend a service request message to the eNB using a signaling radio bearerof the UE, the service request message for requesting establishment ofcellular radio bearers for the UE. In yet another example, the definedresource allocation mode is resource allocation mode 1.

In one example, the one or more processors are further configured todetermine that the UE is limited to using the defined resourceallocation mode based on a system information block (SIB) broadcast fromthe eNB. In another example, the D2D radio bearers are present for theUE when the D2D data is identified to be transmitted to the second UE,wherein the D2D radio bearers operate using a defined radio accesstechnology (RAT) standard. In yet another example, the D2D data isgenerated by a D2D application on the UE.

In one example, the D2D radio bearers are present when the UE is in theRRC idle mode. In another example, the UE can operate in an EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN). In addition, theone or more processors can be further configured to send an RRCconnection request message to the eNB during the RRC connectionestablishment procedure, the RRC connection request message including anindication that the UE is to switch to the RRC connected mode in orderto perform D2D communications. In one configuration, the UE is barredfrom performing the D2D communications for a defined period of time whenthe eNB is enforcing access class barring for the UE.

Another example provides functionality 700 of a user equipment (UE)operable to perform device-to-device (D2D) communications, as shown inthe flow chart in FIG. 7. The functionality can be implemented as amethod or the functionality can be executed as instructions on amachine, where the instructions are included on at least one computerreadable medium or one non-transitory machine readable storage medium.The UE can include one or more processors configured to identify D2Ddata to be transmitted from the UE while the UE is in a radio resourcecontrol (RRC) connected mode with an evolved node B (eNB), as in block710. The UE can include one or more processors configured to determinethat the UE is limited to using a defined resource allocation mode totransmit the D2D data, as in block 720. The UE can include one or moreprocessors configured to send an RRC configuration request message tothe eNB, as in block 730. The UE can include one or more processorsconfigured to receive an RRC connection reconfiguration message from theeNB, the RRC connection reconfiguration message including one or moreconfiguration parameters for the defined resource allocation mode, as inblock 740. The UE can include one or more processors configured to senda buffer status report (BSR) to the eNB in accordance with the one ormore configuration parameters, as in block 750. The UE can include oneor more processors configured to receive an uplink (UL) grant from theeNB for transmission of the D2D data from the UE, as in block 760. TheUE can include one or more processors configured to send the D2D datausing the UL grant provided by the eNB, the D2D data being transmittedfrom the UE using D2D radio bearers of the UE, as in block 770.

In one example, the one or more configuration parameters in the RRCconnection reconfiguration message include at least one of a periodicD2D BSR timer or a D2D BSR retransmission timer. In another example, theRRC configuration request message includes a D2D resource requestindicator information element (IE) ora D2D configuration requestindicator IE. In yet another example, the one or more processors can befurther configured to send the RRC configuration request message to theeNB using a signaling radio bearer of the UE. In one configuration, theD2D radio bearers are present for the UE when the D2D data is identifiedto be transmitted to the second UE, wherein the D2D radio bearersoperate using a defined radio access technology (RAT) standard.

Another example provides a method 800 for performing device-to-device(D2D) communications, as shown in the flow chart in FIG. 8. The methodcan be executed as instructions on a machine, where the instructions areincluded on at least one computer readable medium or one non-transitorymachine readable storage medium. The method can include the operation ofidentifying, at a user equipment (UE), D2D data to be communicated to adestination UE, the D2D data being identified when the UE is in a radioresource control (RRC) idle mode, as in block 810. The method caninclude the operation of determining that the UE is limited to using adefined resource allocation mode to communicate the D2D data to thedestination UE, as in block 820. The method can include the operation ofinitiating a service request procedure at the UE, the service requestprocedure triggering the UE to perform an RRC connection establishmentprocedure with an evolved node B (eNB) to switch the UE from the RRCidle mode to an RRC connected mode, as in block 830. The method caninclude the operation of receiving an uplink (UL) grant from the eNB forcommunicating the D2D data to the destination UE, as in block 840. Themethod can include the operation of sending the D2D data to thedestination UE using the UL grant provided by the eNB, the D2D databeing communicated to the destination UE using D2D radio bearers of theUE, as in block 850.

In one example, the method can include the operation of receiving, atthe UE, the UL grant from the eNB in response to sending a buffer statusreport (BSR) from the UE to the eNB, the BSR being sent to the eNB afterthe UE has switched to the RRC connected mode. In another example, themethod can include the operation of sending the BSR from the UE to theeNB using one or more configuration parameters associated with thedefined resource allocation mode, the one or more configurationparameters including at least one of a periodic D2D BSR timer or a D2DBSR retransmission timer. In yet another example, the method can includethe operation of sending a service request message from the UE to theeNB using a signaling radio bearer of the UE, the signaling radio bearerbeing established for the UE during the RRC connection establishmentprocedure, the service request message for establishing cellular radiobearers for the UE. In addition, the method can include the operation ofdetermining that the UE is limited to using the defined resourceallocation mode based on a system information block (SIB) broadcast fromthe eNB. In one configuration, the method can include the operation ofperforming cell reselection based on whether neighboring cells of the UEsupport D2D communications.

FIG. 9 provides an example illustration of the wireless device, such asan user equipment (UE), a mobile station (MS), a mobile wireless device,a mobile communication device, a tablet, a handset, or other type ofwireless device. The wireless device can include one or more antennasconfigured to communicate with a node, macro node, low power node (LPN),or, transmission station, such as a base station (BS), an evolved Node B(eNB), a baseband unit (BBU), a remote radio head (RRH), a remote radioequipment (RRE), a relay station (RS), a radio equipment (RE), or othertype of wireless wide area network (WWAN) access point. The wirelessdevice can be configured to communicate using at least one wirelesscommunication standard including 3GPP LTE, WiMAX, High Speed PacketAccess (HSPA), Bluetooth, and WiFi. The wireless device can communicateusing separate antennas for each wireless communication standard orshared antennas for multiple wireless communication standards. Thewireless device can communicate in a wireless local area network (WLAN),a wireless personal area network (WPAN), and/or a WWAN.

FIG. 9 also provides an illustration of a microphone and one or morespeakers that can be used for audio input and output from the wirelessdevice. The display screen can be a liquid crystal display (LCD) screen,or other type of display screen such as an organic light emitting diode(OLED) display. The display screen can be configured as a touch screen.The touch screen can use capacitive, resistive, or another type of touchscreen technology. An application processor and a graphics processor canbe coupled to internal memory to provide processing and displaycapabilities. A non-volatile memory port can also be used to providedata input/output options to a user. The non-volatile memory port canalso be used to expand the memory capabilities of the wireless device. Akeyboard can be integrated with the wireless device or wirelesslyconnected to the wireless device to provide additional user input. Avirtual keyboard can also be provided using the touch screen.

Various techniques, or certain aspects or portions thereof, can take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, non-transitory computerreadable storage medium, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing thevarious techniques. Circuitry can include hardware, firmware, programcode, executable code, computer instructions, and/or software. Anon-transitory computer readable storage medium can be a computerreadable storage medium that does not include signal. In the case ofprogram code execution on programmable computers, the computing devicecan include a processor, a storage medium readable by the processor(including volatile and non-volatile memory and/or storage elements), atleast one input device, and at least one output device. The volatile andnon-volatile memory and/or storage elements can be a RAM, EPROM, flashdrive, optical drive, magnetic hard drive, solid state drive, or othermedium for storing electronic data. The node and wireless device canalso include a transceiver module, a counter module, a processingmodule, and/or a clock module or timer module. One or more programs thatcan implement or utilize the various techniques described herein can usean application programming interface (API), reusable controls, and thelike. Such programs can be implemented in a high level procedural orobject oriented programming language to communicate with a computersystem. However, the program(s) can be implemented in assembly ormachine language, if desired. In any case, the language can be acompiled or interpreted language, and combined with hardwareimplementations.

It should be understood that many of the functional units described inthis specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule can be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module can also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

Modules can also be implemented in software for execution by varioustypes of processors. An identified module of executable code can, forinstance, comprise one or more physical or logical blocks of computerinstructions, which can, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but can comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code can be a single instruction, or manyinstructions, and can even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data can be identified and illustrated hereinwithin modules, and can be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data can becollected as a single data set, or can be distributed over differentlocations including over different storage devices, and can exist, atleast partially, merely as electronic signals on a system or network.The modules can be passive or active, including agents operable toperform desired functions.

As used herein, the term “processor” can include general purposeprocessors, specialized processors such as VLSI, FPGAs, and other typesof specialized processors, as well as base band processors used intransceivers to send, receive, and process wireless communications.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials can be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention can be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as defactoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics canbe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of layouts, distances, network examples, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, layouts, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

What is claimed is:
 1. A user equipment (UE) operable to performdevice-to-device (D2D) communications, the UE having one or moreprocessors configured to: identify D2D data to be transmitted from theUE using a D2D radio bearer of the UE, the D2D data being identifiedwhen the UE is in a radio resource control (RRC) idle mode; determinethat the UE is limited to using a defined resource allocation mode tocommunicate the D2D data from the UE; initiate a service requestprocedure at a non-access stratum (NAS) of the UE, the service requestprocedure triggering an RRC layer of the UE to perform an RRC connectionestablishment procedure with an evolved node B (eNB) to switch the UEfrom the RRC idle mode to an RRC connected mode; receive an uplink (UL)grant from the eNB for transmission of the D2D data from the UE; andsend the D2D data using the UL grant provided by the eNB, the D2D databeing transmitted from the UE using the D2D radio bearer of the UE. 2.The UE of claim 1, wherein the one or more processors are furtherconfigured to receive the UL grant from the eNB in response to sending abuffer status report (BSR) from a medium access control (MAC) layer ofthe UE to the eNB, the BSR being sent to the eNB after the UE hasswitched to the RRC connected mode.
 3. The UE of claim 2, wherein theone or more processors are further configured to use one or moreconfiguration parameters associated with the defined resource allocationmode for sending the BSR from the MAC layer of the UE to the eNB, theone or more configuration parameters including at least one of aperiodic D2D BSR timer or a D2D BSR retransmission timer.
 4. The UE ofclaim 1, wherein the one or more processors are further configured toperform the RRC connection establishment procedure at the RRC layer ofthe UE in order to create a signaling radio bearer for the UE.
 5. The UEof claim 1, wherein the one or more processors are further configured tosend a service request message to the eNB using a signaling radio bearerof the UE, the service request message for requesting establishment ofcellular radio bearers for the UE.
 6. The UE of claim 1, wherein thedefined resource allocation mode is resource allocation mode
 1. 7. TheUE of claim 1, wherein the one or more processors are further configuredto determine that the UE is limited to using the defined resourceallocation mode based on a system information block (SIB) broadcast fromthe eNB.
 8. The UE of claim 1, wherein the D2D radio bearers are presentfor the UE when the D2D data is identified to be transmitted from theUE, wherein the D2D radio bearers operate using a defined radio accesstechnology (RAT) standard.
 9. The UE of claim 1, wherein the D2D data isgenerated by a D2D application on the UE.
 10. The UE of claim 1, whereinthe D2D radio bearers are present when the UE is in the RRC idle mode.11. The UE of claim 1, wherein the UE operates in an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN).
 12. The UE of claim 1,wherein the one or more processors are further configured to send an RRCconnection request message to the eNB during the RRC connectionestablishment procedure, the RRC connection request message including anindication that the UE is to switch to the RRC connected mode in orderto perform D2D communications.
 13. The UE of claim 1, wherein the UE isbarred from performing the D2D communications for a defined period oftime when the eNB is enforcing access class barring for the UE.
 14. Auser equipment (UE) operable to perform device-to-device (D2D)communications, the UE having one or more processors configured to:identify D2D data to be transmitted from the UE while the UE is in aradio resource control (RRC) connected mode with an evolved node B(eNB); determine that the UE is limited to using a defined resourceallocation mode to transmit the D2D data; send an RRC configurationrequest message to the eNB; receive an RRC connection reconfigurationmessage from the eNB, the RRC connection reconfiguration messageincluding one or more configuration parameters for the defined resourceallocation mode; send a buffer status report (BSR) to the eNB inaccordance with the one or more configuration parameters; receive anuplink (UL) grant from the eNB for transmission of the D2D data from theUE; and send the D2D data using the UL grant provided by the eNB, theD2D data being transmitted from the UE using D2D radio bearers of theUE.
 15. The UE of claim 14, wherein the one or more configurationparameters in the RRC connection reconfiguration message include atleast one of a periodic D2D BSR timer expiry or a D2D BSR retransmissiontimer.
 16. The UE of claim 14, wherein the RRC configuration requestmessage includes a D2D resource request indicator information element(IE) or a D2D configuration request indicator IE.
 17. The UE of claim14, wherein the one or more processors are further configured to sendthe RRC configuration request message to the eNB using a signaling radiobearer of the UE.
 18. A method for performing device-to-device (D2D)communications, the method comprising: identifying, at a user equipment(UE), D2D data to be communicated to a destination UE, the D2D databeing identified when the UE is in a radio resource control (RRC) idlemode with an evolved node B (eNB); determining that the UE is limited tousing a defined resource allocation mode to communicate the D2D data tothe destination UE; initiating a service request procedure at the UE,the service request procedure triggering the UE to perform an RRCconnection establishment procedure with the eNB to switch the UE fromthe RRC idle mode to an RRC connected mode; receiving an uplink (UL)grant from the eNB for communicating the D2D data to the destination UE;and sending the D2D data to the destination UE using the UL grantprovided by the eNB, the D2D data being communicated to the destinationUE using D2D radio bearers of the UE.
 19. The method of claim 18,further comprising receiving, at the UE, the UL grant from the eNB inresponse to sending a buffer status report (BSR) from the UE to the eNB,the BSR being sent to the eNB after the UE has switched to the RRCconnected mode.
 20. The method of claim 19, further comprising sendingthe BSR from the UE to the eNB using one or more configurationparameters associated with the defined resource allocation mode, the oneor more configuration parameters including at least one of a periodicD2D BSR timer or a D2D BSR retransmission timer.